The Swedish Pat. No. 221 188 discloses a method and an apparatus for cleaning chopped cellulose chip material from accompanying foreign particles. The apparatus comprises a dewatering device equipped with a worm conveyor which suitably is inclined and surrounded by a perforated wall. During the course of the chip being fed upwards in the worm conveyor finer impurities such as sand particles are separated. The separated particles pass through the perforated wall together with the water and are fed through a conduit to a sand trap. The perforations of the partition wall are adapted to the size of the impurities which shall be removed, which means that the size of the perforations is chosen such that the chips essentially cannot pass therethrough but substantially proceed upwards and are delivered to an outlet. Due to the fact that the chip material is fed in at one end and discharged at the other end without being able to pass through the perforated wall the bulk of chip material in the helicoidal passage-way through the worm conveyor will be comparatively compact. Nor does the worm to any significant extent tumble around the bulk of chips in the conveyor, and therefore the washing of the chips during the transportation of same through the conveyor will not be highly efficient.
The Swedish Pat. No. 171 489 discloses an apparatus for drying malt or other lump material. The apparatus comprises a rotatable cylindric drum through which the material to be dried is brought to pass from one gable to the other. The rotating drum is surrounded by a fixed drum so that a sectioned annular space is formed between the drums. Air for drying the material in the inner drum is fed in and led away through the semi-circular channels in the annular space. Further there is provided a central worm in the inner drum for conveying the material. The apparatus has i.a. the limitation that the outer drum excludes the possibility of treating material also outside the rotating drum simultaneous with the treatment of material inside the drum. The apparatus also is based on the principle that the apertures in the perforated drum are so small that only the treatment fluid, in this case air, can pass through the apertures but not the material to be treated. The latter therefore cannot pass in or out through the cylindrical wall of the drum during the treatment which renders any homogenous feeding-in of new material along the perforated length of the drum impossible at the same time as finished material is discharged through the end of the drum.
In certain respects similar but in still higher degree closed systems are shown in the Norwegian Pat. No. 27 159 and the Danish Pat. No. 15 876.
Further there is disclosed in the Swedish Pat. No. 398 633 an apparatus for discharging vessels. The apparatus comprises a vertical fixed non-perforated drum with a central worm conveyor. The shaft of the worm conveyor is perforated so that compressed air or other fluid can be injected through the shaft into the helicoidal passage way of the conveyor which facilitates the transportation through the drum. But due to the fact that the drum is fixed it is nor by means of this apparatus as in the apparatus according to the Swedish Pat. No. 221 188 achieved any tumbling action, and as the apparatus moreover is totally encased, i.e. non-perforated, there is nor achieved any interaction with or affect upon the environment of the drum.